Abstract:

A computational study of free, heated jet flow and resultant far-field sound was performed using large-eddy simulation (LES) and Lighthill's acoustic analogy. A subgrid scale model for small-scale compressible turbulence was developed using a combination of the popular Smagorinsky model and a deductive model. The primary objective is to address large Reynolds number (Re), high subsonic (compressible) flow with realistic geometries more representative of aircraft engine exhausts than typically considered using direct numerical simulation (DNS). Flow field fluctuations are stored over a period of time and used to calculate rms turbulence within the computational domain. The far-field sound and directivity is computed using the time-derivative form of Lighthill's source--integral result formulated in terms of quadrupole sources from the simulated flow field, which is integrated in time and contains the fluctuations set up by the time-varying stress tensor. A simulation for a WR19-4 turbofan engine exhaust (Re(approximately equal to)2x10[sup 6] based on exit velocity and diameter) is presented, and propagated jet noise results are compared with experimental acoustics data. Methods to account for effects of source convection and thermal refraction to obtain realistic frequency spectra and directivity are considered.